JP2014169655A - Egr device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an EGR device capable of preventing a soot compound from attaching to and accumulating on an EGR pipe, an EGR cooler and an EGR valve.SOLUTION: An EGR device in which a part of exhaust gas 8 is extracted from an exhaust passage of an engine 1 through an EGR pipe 11 to be recirculated into an intake passage as recirculation gas 8' includes an exhaust throttle means (variable nozzle turbocharger 2) for throttling flow of the exhaust gas 8 in a downstream side of an extracting position of the recirculation gas 8' in the exhaust passage, and includes a control device 21 for executing a scavenging mode for fully opening an EGR valve 12 and throttling the exhaust throttle means so as to forcibly increase a flow rate and flow velocity of the recirculation gas 8' when a condition to have the risk of accumulation of a soot compound on the EGR pipe 11, an EGR cooler 13 and the EGR valve 12 is established.

Description

  The present invention relates to an EGR device.

  Conventionally, in an automobile engine or the like, a part of exhaust gas is extracted as a recirculation gas from the exhaust side and returned to the intake side, and the recirculation gas returned to the intake side suppresses combustion of fuel in the engine and burns. Some have implemented so-called exhaust gas recirculation (EGR) in which the generation of NOx is reduced by lowering the temperature.

  In general, when this type of exhaust gas recirculation is performed, an EGR pipe is used between an appropriate position of the exhaust passage extending from the exhaust manifold to the exhaust pipe and an appropriate position of the intake passage extending from the intake pipe to the intake manifold. By connecting and opening / closing an EGR valve provided in the middle of the EGR pipe, the recirculated gas is recirculated from the exhaust side to the intake side by utilizing a differential pressure.

  Here, when the recirculated gas that is recirculated to the engine is cooled in the middle of the EGR pipe, the temperature of the recirculated gas decreases and the volume of the recirculated gas decreases, thereby reducing the combustion temperature without significantly reducing the engine output. Since generation of NOx can be reduced, a shell and tube type EGR cooler is provided in the middle of the EGR pipe for recirculating the reflux gas.

  As prior art document information related to this type of EGR apparatus, there are the following Patent Documents 1 and 2 and the like.

JP 2002-39019 A JP 2008-280867 A

  However, in vehicles with a mode of operation in which light-duty low-speed driving and stopping are repeated intermittently (such as buses that operate in congested routes in central Tokyo and trucks that perform delivery operations in areas where delivery destinations are dense), exhaust gas As the operation state with low flow velocity and temperature continues for a long time, soot compounds adhere to and accumulate on the EGR pipe, the EGR cooler and the EGR valve in the middle of the EGR pipe, and the EGR pipe flow path cross-sectional area is reduced. There is a possibility that problems such as a decrease in efficiency and clogging of the cooler, malfunction of the EGR valve, and the like may occur.

  That is, in an operating state where the exhaust gas flow rate and temperature are low, the flow rate and temperature of the recirculation gas, which is a part of the exhaust gas, are low, but when the recirculation gas flow rate is low, the carbonaceous fraction is recirculated. If the temperature of the reflux gas is low, the SOF component (Soluble Organic Fraction) consisting of high-boiling hydrocarbon components derived from fuel is wet. Since it remains without being volatilized on the flow path wall surface, the soot adhering to the wet flow path wall surface is not easily blown away, and there is a concern that it will grow as a soot compound as it is.

  In particular, at the outlet side of the EGR cooler, the low-temperature reflux gas is originally cooled with water, resulting in a significant decrease in temperature. It has been found that a lot of soot compounds tend to deposit and accumulate after the outlet of the EGR cooler.

  At this time, if a particulate filter is installed in the middle of the exhaust pipe and the control to regenerate the particulate filter is started, the situation becomes worse, and post injection (near compression top dead center) on the engine side. Fuel injection added at the timing of non-ignition later than the compression top dead center following the main injection of fuel is performed, so that the SOF content increases and highly reactive carbonization that causes the soot compound There is a concern that the amount of hydrogen-based gas will increase and the deposition of soot compounds will become more prominent.

  Incidentally, the control for regenerating the particulate filter referred to here means that fuel is added by post injection on the engine side to the oxidation catalyst arranged in the preceding stage of the particulate filter, and the added fuel (HC) is added to the above-mentioned fuel (HC). This means that the oxidation reaction is performed with an oxidation catalyst, and the catalyst bed temperature of the particulate filter immediately after the reaction heat is increased to burn and remove the collected particulates.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an EGR device capable of preventing the soot compound from adhering and accumulating on an EGR pipe, an EGR cooler, and an EGR valve.

  The present invention relates to an EGR device in which a part of exhaust gas is extracted from an exhaust passage of an engine through an EGR pipe and recirculated as a recirculation gas to an intake passage, and the recirculation gas is removed from the exhaust passage in the exhaust passage. An exhaust throttle means for restricting the flow of exhaust gas on the downstream side is provided, and the EGR valve is opened when a condition that may cause deposition of soot compounds on the EGR pipe, the EGR cooler in the middle of the EGR pipe, and the EGR valve is satisfied. And a control device that executes a scavenging mode for forcibly increasing the flow rate and flow rate of the recirculated gas by opening the exhaust throttle means and narrowing the exhaust throttle means.

  Thus, in this way, when a condition that may cause deposition of soot compounds is established in the EGR pipe, the EGR cooler, and the EGR valve, the control device opens the EGR valve to a specified opening and the exhaust throttle The means is squeezed to forcibly increase the flow rate and flow rate of the reflux gas, and the vigorous flow of the reflux gas scavenges the soot and hydrocarbon gas that is the precursor of the soot compound, and the EGR pipe In addition, the generation of soot compounds in the EGR cooler and the EGR valve is prevented.

  Here, the condition that the accumulation of soot compound is concerned about the EGR pipe, the EGR cooler, and the EGR valve is, for example, the case where the accumulated time when the outlet gas temperature of the EGR cooler does not exceed the predetermined temperature exceeds the specified time. It is also possible that particulate filter regeneration control is performed in a light load operation state at a predetermined rotational speed or less, but if any condition is concerned about the accumulation of soot compounds, what event is the standard The condition itself may be arbitrarily determined.

  In addition, a variable nozzle turbocharger that can adjust the nozzle vane opening of the turbine is mounted on the engine so that part of the exhaust gas is extracted from the exhaust manifold as recirculation gas and recirculated near the inlet of the intake manifold. When configured, the variable nozzle turbocharger is preferably used as an exhaust throttle means.

  In this way, the existing variable nozzle turbocharger can be used effectively without changing the control logic of the variable nozzle turbocharger effectively without providing a new exhaust throttle means. It becomes possible.

  Furthermore, in the present invention, an electric heater is provided at at least one of the inlet and outlet of the EGR cooler, and the control device is configured to execute the heating of the reflux gas by the electric heater when the scavenging mode is executed. Is also possible.

  In this way, the reflux gas is heated by the electric heater to raise the outlet gas temperature of the EGR cooler, and the SOF content derived from the fuel can be volatilized as much as possible to suppress the residue on the channel wall surface. In addition, the flow path wall surface can be held in a dry state to facilitate the blow-off of the apportioned portion.

  In the present invention, a cooling water throttle means for reducing the flow rate of the cooling water sucked into and discharged from the EGR cooler is provided, and the cooling water flow rate is narrowed down by the cooling water throttle means when the scavenging mode is executed. It is also possible to configure a control device.

  In this way, the cooling efficiency in the EGR cooler is reduced by narrowing the flow rate of the cooling water to increase the outlet gas temperature of the EGR cooler, and the SOF content derived from the fuel is volatilized as much as possible to remain on the channel wall surface. Therefore, it is possible to keep the flow path wall surface in a dry state and facilitate the blow-off of the apportionment.

  According to the EGR device of the present invention described above, various excellent effects as described below can be obtained.

  (I) According to the invention described in claim 1 of the present invention, the flow rate and flow rate of the reflux gas are forcibly increased under conditions where the deposition of soot compounds is a concern on the EGR pipe, the EGR cooler, and the EGR valve, The vigorous flow of the reflux gas can scavenge soot and hydrocarbon gas, which are precursors of soot compounds, so that soot compounds adhere to and accumulate on the EGR pipe, EGR cooler and EGR valve. Can be prevented.

  (II) According to the invention described in claim 2 of the present invention, the existing variable nozzle turbocharger can be effectively used without newly providing an exhaust throttle means, and the variable nozzle turbocharger can be used. Since it can be implemented at low cost simply by changing the control logic, the implementation cost can be greatly reduced.

  (III) According to the invention described in claim 3 of the present invention, the reflux gas can be heated by the electric heater and the outlet gas temperature of the EGR cooler can be raised, so that the SOF content derived from the fuel is volatilized as much as possible. Therefore, it is possible to suppress the residue on the channel wall surface, and it is possible to keep the channel wall surface in a dry state and facilitate the blow-off of apportionment.

  (IV) According to the invention described in claim 4 of the present invention, since the cooling efficiency in the EGR cooler can be lowered by narrowing the flow rate of the cooling water and the outlet gas temperature of the EGR cooler can be raised, The SOF component can be volatilized as much as possible to suppress the residue on the flow channel wall surface, and the flow channel wall surface can be maintained in a dry state to facilitate the blowing off of the soot.

It is the schematic which shows an example of the form which implements this invention. It is a flowchart which shows the specific control procedure in the control apparatus of FIG.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an example of an embodiment of the present invention, in which 1 in FIG. 1 shows an engine that is a diesel engine, and the engine 1 shown here can adjust the nozzle vane opening of the turbine 2b. The variable nozzle type turbocharger 2 is mounted, and the intake air 3 guided from an air cleaner (not shown) is sent to the compressor 2a of the variable nozzle type turbocharger 2 through the intake pipe 4, and the intake air 3 pressurized by the compressor 2a is supplied. The air is sent to the intercooler 5 for cooling, and the intake air 3 is further guided from the intercooler 5 to the intake manifold 6 to be distributed to each cylinder 7 of the engine 1.

  Further, the exhaust gas 8 discharged from each cylinder 7 of the engine 1 is sent to the turbine 2b of the variable nozzle type turbocharger 2 through the exhaust manifold 9, and the exhaust gas 8 driving the turbine 2b is sent through the exhaust pipe 10. It is designed to be discharged outside the vehicle.

  An end portion of the exhaust manifold 9 in the arrangement direction of the cylinders 7 and the vicinity of the inlet of the intake manifold 6 are connected by an EGR pipe 11, and a part of the exhaust gas 8 is extracted from the exhaust manifold 9 and recirculated. The gas 8 ′ can be recirculated to the vicinity of the inlet of the intake manifold 6.

  Here, in the middle of the EGR pipe 11, an EGR valve 12 for adjusting the recirculation amount of the recirculated gas 8 'and an EGR cooler 13 for cooling the recirculated recirculated gas 8' are equipped. In the EGR cooler 13, the temperature of the reflux gas 8 ′ can be lowered by heat exchange between the cooling water 14 and the reflux gas 8 ′.

  The cooling water 14 for cooling the reflux gas 8 ′ is introduced into the EGR cooler 13 through the water supply pipe 15 and discharged from the EGR cooler 13 through the drain pipe 16. Is provided with a cooling water throttle valve 17 as a cooling water throttle means for reducing the flow rate of the cooling water 14, and the drain pipe 16 is provided with a cooling water temperature sensor 18 for detecting the temperature of the cooling water 14. .

  Further, in this embodiment, an electric heater 19 is provided at the inlet of the EGR cooler 13 so that the reflux gas 8 ′ can be heated by the electric heater 19 to forcibly raise the temperature of the reflux gas 8 ′. A temperature sensor 20 is provided at the outlet of the EGR cooler 13 for detecting the temperature of the reflux gas 8 ′ (outlet gas temperature).

  The detected values of the temperature sensor 20 and the coolant temperature sensor 18 are input to a control device 21 that also serves as an engine control computer (ECU: Electronic Control Unit). Control of the nozzle-type turbocharger 2, the EGR valve 12, and the cooling water throttle valve 17 is performed.

  In other words, the control device 21 opens the EGR valve 12 and opens the variable nozzle when a condition that causes deposition of soot compounds on the EGR pipe 11, EGR cooler 13, and EGR valve 12 is satisfied. The scavenging mode for forcibly increasing the flow rate and flow velocity of the recirculation gas 8 ′ is performed by narrowing the nozzle vane opening of the turbine 2 b of the turbocharger 2.

  More specifically, in the normal control of the EGR valve 12 by the control device 21, the target air amount is determined according to the operating state, and the EGR sensor 22 uses the air amount actually measured by the airflow sensor 22 as the target air amount. The valve 12 is controlled. However, only when the scavenging mode is executed, the control for fully opening the EGR valve 12 away from the normal control is executed. ing.

  Further, in the normal control of the variable nozzle turbocharger 2 by the control device 21, the turbine 2b has a low driving force, so that it is difficult to take in air, and the turbine 2b rotates too much and air may be taken in excessively. When the scavenging mode is being executed, control is performed so that the capacity can be changed appropriately in the high-speed operation area where there is a leak and the supercharging characteristic emphasizing low speed and the supercharging characteristic emphasizing high speed can be used properly. However, the control is executed to narrow down the nozzle vane opening on the turbine 2b side so that the variable nozzle turbocharger 2 can be used as the exhaust throttle means apart from the normal control.

  Moreover, in the present embodiment, when the scavenging mode is executed, the electric heater 19 at the inlet of the EGR cooler 13 is energized by the control device 21, and the reflux gas 8 ′ is also heated by the electric heater 19. In addition, the flow rate of the cooling water 14 is also reduced by the cooling water throttle valve 17.

  In FIG. 1, reference numeral 23 denotes a particulate filter, and 24 denotes an oxidation catalyst arranged in the preceding stage. When the estimated value of the accumulated amount of particulates in the particulate filter 23 exceeds a specified value, the control is performed. The regeneration control is executed by the device 21. More specifically, fuel is added to the exhaust gas 8 by post injection on the engine 1 side, and the added fuel (HC) is used as the oxidation catalyst. By performing the oxidation reaction at 24, the catalyst bed temperature of the particulate filter 23 immediately after the reaction heat is raised, and the collected particulates are burned and removed.

  Here, in the present embodiment, the outlet gas temperature of the EGR cooler 13 does not exceed a predetermined temperature (for example, 90 ° C.) as a condition that the deposition of soot compounds is concerned about the EGR pipe 11, the EGR cooler 13, and the EGR valve 12. The case where the accumulated filter traveled over a specified time (for example, 1 hour) and the regeneration control of the particulate filter 23 in a light load operation state at a predetermined rotation speed (for example, 1200 rpm) or less is employed. The scavenging mode is executed when either of these two conditions is satisfied. However, the condition in which the soot compound is a concern may be based on any event, The conditions themselves can be determined arbitrarily.

  Further, in this embodiment, the scavenging mode is divided into two stages. First, the EGR valve 12 is fully opened and the nozzle vane opening on the turbine 2b side is narrowed while simultaneously using heating of the electric heater 19 and narrowing of the cooling water 14. The heated scavenging mode is performed, and then the flow velocity scavenging mode is performed in which only the EGR valve 12 is fully opened and the nozzle vane opening on the turbine 2b side is narrowed down. At this time, the electric heater 19 is heated so that the detection value of the temperature sensor 20 (the outlet gas temperature of the EGR cooler 13) becomes a predetermined temperature (for example, 120 ° C.). The narrowing is performed so that the detection value of the cooling water temperature sensor 18 (the temperature of the cooling water 14 in the drain pipe 16) falls below a predetermined temperature (for example, 90 ° C.).

  The specific control procedure in the control device 21 is as shown in the flowchart of FIG. 2. First, in step S1, the accumulated time Ice traveled without the outlet gas temperature Tgo of the EGR cooler 13 exceeding 90 ° C. is reset. In the next step S2, the regeneration control Rce of the particulate filter 23 is performed in the light load operation state where the integrated time Ice exceeds 1 hour or the engine speed Ne is 1200 rpm or less. When one of the conditions is satisfied, the process proceeds to the next step S3 to start the heating and scavenging mode, and in the next step S4, it is confirmed that the heating and scavenging mode has elapsed for 5 minutes. After that, in step S5, the flow rate scavenging mode is started, and in the next step S6, the flow rate scavenging mode is changed over to 3 minutes. It is to return to the start and ended it after confirming.

  In this way, when a condition that may cause deposition of soot compounds in the EGR pipe 11, EGR cooler 13, and EGR valve 12 is satisfied, the control device 21 fully opens the EGR valve 12 and the variable nozzle turbocharger. Since the nozzle vane opening degree of the turbine 2b of No. 2 is narrowed down and the flow rate and flow velocity of the reflux gas 8 'are forcibly increased, the vigorous flow of the reflux gas 8' causes the distribution of the precursor of the soot compound. As a result, scavenging of the hydrocarbon gas and the EGR pipe 11, the EGR cooler 13, and the EGR valve 12 are prevented from being generated.

  At this time, if the heating of the electric heater 19 and the narrowing of the cooling water 14 are used in combination as in the heating and scavenging mode described above, the reflux gas 8 ′ is heated by the electric heater 19 and the outlet gas temperature of the EGR cooler 13 is increased. In addition, since the cooling efficiency in the EGR cooler 13 can be reduced by reducing the flow rate of the cooling water 14 and the outlet gas temperature of the EGR cooler 13 can be raised, the SOF content derived from the fuel is volatilized as much as possible. It is possible to suppress the remaining on the channel wall surface and keep the channel wall surface in a dry state, and it is possible to facilitate the blow-off of apportionment by executing the flow rate scavenging mode following this. Become.

  Therefore, according to the above embodiment, the flow rate and flow rate of the reflux gas 8 'are forcibly increased under the condition that the deposition of the soot compound is concerned on the EGR pipe 11, the EGR cooler 13, and the EGR valve 12, and the reflux gas 8 Because of the vigorous flow, it is possible to scavenge soot and hydrocarbon gas, which are precursors of soot compounds, so that soot compounds adhere to and accumulate on the EGR pipe 11, EGR cooler 13 and EGR valve 12. Can be prevented.

  In addition, the existing variable nozzle turbocharger 2 can be used effectively without newly providing an exhaust throttling means, and can be implemented at low cost simply by changing the control logic of the variable nozzle turbocharger 2. Therefore, the implementation cost can be greatly reduced.

  However, the exhaust throttle means is not necessarily limited to utilizing the variable nozzle type turbocharger 2, and an exhaust brake 25 or the like downstream from the turbine 2b may be utilized as the exhaust throttle means. Even if a means is newly provided, there is no particular problem other than cost.

  Furthermore, the combined use of the heating of the reflux gas 8 ′ by the electric heater 19 and the narrowing of the cooling water 14 by the cooling water throttle valve 17 can increase the outlet gas temperature of the EGR cooler 13. The SOF component can be volatilized as much as possible to suppress the residue on the flow channel wall surface, and the flow channel wall surface can be maintained in a dry state to facilitate the blowing off of the soot.

  The EGR device of the present invention is not limited to the above-described embodiment. In this embodiment, it is assumed that the EGR valve is fully opened in the scavenging mode assuming a general traveling environment. However, when a special driving environment with low oxygen concentration such as high places is assumed, the engine performance is significantly reduced (power reduction, PM emission increase) by fully opening the EGR valve in the scavenging mode. Therefore, the EGR valve in the scavenging mode should be opened to an appropriate specified opening determined according to the assumed traveling environment. In addition, in the drawing, the EGR cooler inlet Although the case where an electric heater is provided on the side is illustrated, it may be provided on the outlet side, may be provided on both the inlet and outlet, and the cooling water throttling means may be provided on either the water supply pipe or the drain pipe. What can be provided, Heating of the recirculation gas by the air heater and throttling of the cooling water by the cooling water throttle valve may be used in combination as needed, and other various modifications may be made without departing from the scope of the present invention. It is.

1 Engine 2 Variable nozzle turbocharger (exhaust throttle means)
2b Turbine 6 Intake manifold (intake passage)
8 Exhaust gas 8 'Reflux gas 9 Exhaust manifold (exhaust passage)
11 EGR pipe 12 EGR valve 13 EGR cooler 14 Cooling water 17 Cooling water throttle valve (cooling water throttle means)
19 Electric heater 21 Control device

Claims (4)

  An EGR device in which a part of exhaust gas is extracted from an exhaust passage of an engine through an EGR pipe and recirculated as a recirculation gas to an intake passage, and is exhausted downstream of the recirculation gas extraction position in the exhaust passage. An exhaust throttle means for narrowing down the gas flow, and when the condition that causes the accumulation of soot compound on the EGR pipe, the EGR cooler in the middle of the EGR pipe, and the EGR valve is satisfied, the EGR valve is opened to a specified opening degree; An EGR apparatus comprising: a control device that executes a scavenging mode for forcibly increasing the flow rate and flow rate of the reflux gas by narrowing the exhaust throttle means.   A variable nozzle type turbocharger that can adjust the nozzle vane opening of the turbine is installed in the engine, and a part of the exhaust gas is extracted from the exhaust manifold as recirculation gas and recirculated near the inlet of the intake manifold. 2. The EGR apparatus according to claim 1, wherein the variable nozzle type turbocharger is an exhaust throttle means.   The control device is configured to provide an electric heater at least one of an inlet and an outlet of the EGR cooler and to perform heating of the reflux gas by the electric heater at the time of executing the scavenging mode. Or the EGR apparatus of 2.   Provided with a cooling water throttle means for reducing the flow rate of the cooling water that is sucked into and discharged from the EGR cooler, and configured the control device to simultaneously reduce the cooling water flow rate by the cooling water throttle means when the scavenging mode is executed. The EGR device according to claim 1, 2, or 3.

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